In public good games, voluntary contributions tend to start of high and decline as the game is repeated. If high contributors are matched, however, contributions tend to stay high. We propose a formalization predicting that high contributors will selfselect into groups committed to charitable...

We report evidence from a laboratory experiment comparing contributions in public good games played as individuals to contributions made as group representatives. We find that women alter their behaviour more than men. The change is in an out-group friendly direction: while men's contributions...